Each VPN configuration is assigned a group name, which is used to manage
separate Security Associations. Previous advisories have found that when a
VPN endpoint is configured to allow Aggressive Mode IKE negotiations using
PSK, a hash of the PSK can be captured and potentially cracked offline. In
order to successfully crack this hash a correct group name is required.

The above product versions are susceptible to a group name enumeration
vulnerability, because of a difference in the way the device responds to
correct and incorrect group names sent in the initial exchange packet.

Similar to CSCeg00323 and CSCtj96108 where this was possible because of no
response and a response with a DPD payload respectively. It has been found
that it remains possible to distinguish a correct group name by the number
of response packets sent by the device. A correct group name elicits three
attempts to continue the handshake and an additional encrypted phase 2
packet, while the device will only respond twice to an incorrect group.
Enumeration is slow because of the requirement to wait for the responding
packets, but this has been successfully accomplished. Below are examples of
the different responses:

This information can be used to capture and crack a weak PSK if Aggressive
Mode is enabled.

Remediation Steps:
The vendor will be releasing security fixes to the above issues and affected
versions can be patched by installing the 8.4(6) firmware or the 9.1(2)
firmware for the Cisco ASA platform. Administrators with other affected
firmware versions should be aware that this information could be
potentially be revealed and it is recommended that factory default group or
easily guessable group names are not used.

About Trustwave:
Trustwave is the leading provider of on-demand and subscription-based
information security and payment card industry compliance management
solutions to businesses and government entities throughout the world. For
organizations faced with today's challenging data security and compliance
environment, Trustwave provides a unique approach with comprehensive
solutions that include its flagship TrustKeeper compliance management
software and other proprietary security solutions. Trustwave has helped
thousands of organizations--ranging from Fortune 500 businesses and large
financial institutions to small and medium-sized retailers--manage
compliance and secure their network infrastructure, data communications and
critical information assets. Trustwave is headquartered in Chicago with
offices throughout North America, South America, Europe, Africa, China and
Australia. For more information, visit https://www.trustwave.com

About Trustwave SpiderLabs:
SpiderLabs(R) is the advanced security team at Trustwave focused on
application security, incident response, penetration testing, physical
security and security research. The team has performed over a thousand
incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

Disclaimer:
The information provided in this advisory is provided "as is" without
warranty of any kind. Trustwave disclaims all warranties, either express or
implied, including the warranties of merchantability and fitness for a
particular purpose. In no event shall Trustwave or its suppliers be liable
for any damages whatsoever including direct, indirect, incidental,
consequential, loss of business profits or special damages, even if
Trustwave or its suppliers have been advised of the possibility of such
damages. Some states do not allow the exclusion or limitation of liability
for consequential or incidental damages so the foregoing limitation may not
apply.

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